Galvanometer



March 3l, 1942.

F. G. BACK GALVANOMETER Filed Aug; 30, 1940 Patented Mar. 31, 1942oALvANormrnR York, NSY.

Franz G. Back, New York, N. Y., assigner of oneourth to Gastro-PhotorLaboratories, New

Application August 30, 1940, Serial No. 354,796

16 Claims. (Cl. 179-1003) My present invention relates to galvanometersor like instruments adapted to indicate ornrecord electricaloscillations by modulating a light beam. More particularly, myinventionrelates to galvanometers used for producing photographic sound recordson a sound record carrier, e. g., a lm moving with uniform speed. byoscillating in the path of a light beam a light-modulating member inaccordance with the sound oscillations to be recorded.

It is the main object 0i my invention to provide for apparatus of theabove type a new oscillatig member which has no sharp resonancefrequency; the resonance curve of this member should be flat incomparison with the curve of other light-modulating members used untilnow.

It is a further object of my invention to provide a light-modulatingoscillating member of a shape which makes it unnecessary to keep .itunder constant tension and stress, thus avoiding-by using a memberwithout strainexternal influences of temperature changes, of mechanicalvibrations, or the like, on the frequency characteristic of thisoscillating member.

It is another object of my invention to provide a light-modulatingoscillating member of such a shape that it should be easily possible'tochange the frequency characteristic of this member by changing its sizeand the relative dimensions of the parts of which it is composed.

It is still a further objectof my present inventien to use such amodulating member which enables mechanical damping without substantialbraking of the oscillations.

In order to attain the above objects, I propose to combine in anapparatus of the class described a light source being adapted to emit alight beam, a substantially U-shaped oscillating member being made of a`thin metallic strip, said member being arranged in the path of andsubstantially in one plane with said light beam. a stationary support towhich both ends of said U-shaped member are fastened, and means beingadapted to oscillate said oscillating member in direction of the widthof the strip of which it is made.

A preferred embodiment of my light-.modulating means consists in asubstantially U-shaped oscillating member bent of a thin metallic stripand consisting of a front strip, two side strips and two fasteningstrips, forming an angle with said side strips: this oscillating memberis arranged in such a manner that said front strip is in the path ofsaid light; beam and its face is substantially. normal to it.

Furthermore I have found it to be of advantage to provide for thisU-shaped oscillating member a stationary support to which the free endsof the fastening strips are fixedin such a manner as to leave theportions of the fastening strips, which are adjacent to the edges formedby the fastening and side strips, unxed to said stationary support,thereby enabling oscillation of these strip portions.

Further characteristic features of my new new light-modulating systemand the sound recording unit equipped with this system, and advantagesof the improvements proposed by me, will appear from the followingdescription and the accompanying drawing, illustrating one embodiment ofmy invention.

In the drawing:

Fig. 1 shows a cross section of my new galvanometer along line I-i ofFig. 7;

Fig. 2 shows a cross section of my new galvanometer along vline 2-2 ofFig. 7;

Fig. 3 shows a perspective view of the U-shaped oscillating member;

Fig. 4 shows a plane View of the galvanometer along line Ii-li of Fig.1; V

Fig. 5 shows a cross section of the galvanometer along line 5--5 of Fig.l;

Fig'. 6 shows a plane View of the galvanometer along line 6 6;

Fig. '7 shows a plane View vanometer; Figs. 8 to 10 show differentarrangements ol the oscillating member and the slit in the upper poleshoe.l

As shown inFigs. l and 2, the galvanometer consists of an insulatingdisk i to which the U- shaped oscillating member 2 isk fastened by thesmall inner and outer plates 3: theseplates 3 are connected by screws3'. The outer plates serve simultaneously for electrically connectingthe conducting wires il with the oscillating member 2.

In order to prevent contact between the magnetic system ofy thegalvanometer and the small plates 3, a further insulating disk 5 isarranged around these plates.

of the whole gallating member 2.

The magnetic vfield necessary for producing oscillations of the U-shapedmember 2 is produced by th permanent magnets 'l being in inti- This disk5 is provided` with an opening 6 fory the plates 3 and the oscil- U-shaped magnetic field has its lines of force substantially parallel tothe plane of the oscillating member; thereby it causes oscillation ofthis member in accordance with the current oscillations in the electriccircuit to which it is connected by conducting wires il.

The upper pole shoe i@ is covered by a cover lplate l2; they are bothprovided with concentric longitudinal holes i3 and lil, respectively. Inthese longitudinal holes the optical system producing the sharp lightbeam needed for recording purposes can be arranged. Both holes have asquare-shaped cross section, and hole lf3 ends at its lower end in aslit l5; this slit is parallel to the longitudinal direction of member2.

In order to have the possibility to produce the square-shapedlongitudinal hole lil and slit l5 in pole shoe 9, this pole shoeis madeof two pieces and held together by an angular fastening ring 23. Screws2d serve for fixing all parts of the galvanometer -unit to each other.

The light-modulating member consists, as shown in Fig. 3, of a irontstrip it, two side strips il, forming an angle of 96 with the frontstrip, and two fastening strips iii forming also an angle of 99 withsaid side strips. Thefastening plates 3 are provided in such a mannerlas to leave between these plates and the edges l free portions 233,being adapted to oscillate together with the other parts ib and ll ofmember 2. I havefound it very important to fasten member 2 to itssupport in the way described above, because if I nx the side strips ilof the oscillating member directly to the stationary support, I cannotattain oscillations of the lrindneeded for my purpose.

According to my' observations it is of advantage to malte the irontstrip it substantially as long as each or the side strips il', and tomake furthermore the width of the strip of which this member is bent,about one half to one fifth of the length of each of these parts. For anembodiment of my new oscillating member I have used a strip having awidth oi' about 13g", made each of the side strips and the front stripabout 1/4" long; with this oscillating member I attained excellentresults. The thickness of the strip is about 50.001.

I want to stress that I ldo not intend to be i limited to oscillatingmembers having the above described shape only: my pres-ent inventionincludes all possible types of U-shaped members, i. e., 'arc-shapedmembers or members being composed of arc-shaped and plane stripportions.

As shown in Fig. 8, .tor sound recording purposes the front strip l@ canbe provided with two or more cut-outs l, producing thereby sound recordsof the multiple variable-area type on the lm.

Fig. 9 shows= an arrangement with an oscillating member provided withone cut-out, for producing one sound record of the variable area typeonly. In the arrangement shown in Fig. 10 slit and I5 and oscillatingmember! form an acute anarea type, but its width varies along one edgeofthe record only.

For damping the oscillations of member 2 I found it of alvantage toprovide damping material being in contact with one of the stationaryparts of the system and with the outer faces of the side strips Il ofthe oscillating member; for this purpose I `may use a small amount ofcotton wool or the like being provided between the pole shoe 8 andoscillating `member 2. I may also use rubber drops 22 adhering to thestationary pole shoe 8, or plate 3, as well as to the outer faces of theside strips ll. By using these means, unwanted oscillations of member 2may be clamped, without substantially braking its oscillating movement.

For purposes of sound recording a continuously moving lm strip, notshown in the drawing, is arranged under opening 25 in insulating disk i.The conducting Wires d are connected to the electric circuit modulatedin accordance with the sound to be recorded, Due to the combined actionof the magnetic field in which it is arranged and the modulated currentowing through it, the light-modulating member oscillates in accordancewith the sound oscillations to be recorded in the direction indicated byarrow 2t in Fig. 3, i. e. in direction of the width ofthe strip of whichit is made. As the optical system within openings i3 and I4 is arrangedin suchv a manner that the light beam passing through the slit in theupper pole shoe is modulated when member 2 oscillates, it may easily beunderstood that by oscillating this member in accordance with the soundoscillations to be recorded, the shape of the light beam reaching thenlm will be modulated in the same way, i. e. it will also be modulatedin accordance with the sound oscillations `to be recorded.

It will be understood that each of the elements of my newlight-modulating system, or two or more together, may also und a'usefulapplication in other type of apparatus deferring from the type describedabove. It will furthermore be understood that I do not intend to belimited to the 'exact shape of the oscillating member proposed by me,since various modifications and changes in shape, size and relativedimensions may be made without departing in any way from thespirit of myinvention.

Without further analysis the foregoing will so' fully reveal the gist ofmy invention that others can by applying current knowledge readily adaptit for various applications without omitting features, that, from thestandpoint of the prior art fairly constitute essential characteristicsof the generic or specific aspects of my invention, and therefore suchadaptations should and are intended to be comprehended-within themeaning and range of equivalency of the following claims.

What I claim as new and desire to secure by Letters Patent is:

l. In an apparatus of the class described a light source adapted to emita light beam, a substantially U-shaped oscillating member bent of a thinmetallic strip and consisting of a front strip, two sidestrips, and twofastening strips forming an angle with said side strips, saidoscillating member arranged in such a manner that said front strip is inthe path of said light beam and its face is substantially normal to saidlight beam, a stationary support to which the free ends of saidfastening strips are rigidly xed in'such a manneras to leave theportions of said fastening strips which are adjacent to said edgesbetween fastening and side strips, unxed to said lstationary support,and means adapted to oscillate said oscillating member in direction ofthe width of the stripof which it is bent.

A2. In an apparatus of the class described a light source adapted toemit a light beam, a substantially U-shaped oscillatingv member bent ofa thin metallic strip and consisting of a front strip, two side strips,and two fastening strips, said `iasteningL strips arranged at an anglewith -said side strips and forming thereby an edge between saidfastening and said strips, said oscillating member arranged in such amanner that said front strip is in the path of said light beam and itsface is substantially normal to said light beam, a stationary support towhich the free ends of said fastening strips are rigidly xed in such amanner as to leave the portions of said fastening strips, which areadjacent to said edges between fastening and side strips, uniixed tosaid stationary support, enabling thereby oscillation of these freefastening strip portions, and means adapt-edY to oscllate saidoscillating member in direction of the width of the strip of which it isbent.

3. In an apparatus of the class described, a light source adapted toemit a light beam, a substantially U-shaped oscillating member bent ofa'thin metallic strip and including a front strip, two side strips beingsubstantially normal to said front strip, and two fastening strips atythe ends of said side strips being substantially normalto said sidestrips, said oscillating member arranged in such 'a manner that saidfront strip is in the path of said light beam and its face issubstantially normal to said light beam, a stationary support towhich'the free ends of said fastening strips are rigidly fixed in such amanner as to leave the portions of said fastening strips, which areadjacent to said edges between fastening and side strips, unxed to saidstationary support, enabling thereby oscillation of these free fasteningstrip portions, and means adapted to oscillate said oscillating memberin direction of the width of the strip of which it is bent.

4. In an apparatus of the class described, a light source adapted toemita light beam, a substantially .U-shaped oscillating 4member bent of athin metallic strip, and including a plane front strip, two plane sidestrips and two plane fastening strips forming an angle with said sidestrips and being substantially parallel to said front strip, saidoscillating member arranged in such a manner that said plane front stripis in the path of and its face substantially normal to said light beam,a stationary support to which the free ends of said plane fasteningstrips are rigidly fastened in such a manner as to leave the portions ofsaid fastening strips which are adjacent to said edges between fasteningYand side strips, yunxed to said stationary support, and means adaptedto oscillate said oscillating member in direction of the width of thestrip of which it is bent.

5. In an apparatus of the class described, a

light source adapted to emit a light beam, a subi ber arranged in such amanner that said front strip is in the path of and its facesubstantially adjacent to said edges between fastening and side strips,unxed to said stationary support, and means adapted to oscillate saidoscillating member in direction of the'width of the strip of which it isbent.

6. In an apparatus of the class described. a light source adapted toemit a. light beam, a substantially U-shaped oscillating member bent o!a thin metallic strip and including a plane front strip, two plane sidestrips being substantially normal to said front strip, and their lengthbeing substantially equal to the length of said front strip, and twoplane fastening strips forming an angle with said side strips, saidoscillating member arranged in such a manner that said front strip is inthe path of and its face substantially normal to said light beam, astationary support to which the free ends of said plane fastening stripsare rigidly fastened in such a manner as to leave the portions of saidfastening strips which are adjacent to said edges between fastening andside strips, uniixed to said stationary support,

and means adapted to oscillate said oscil1at-'.

ing member in direction of the width of the strip of which it is bent.

7. In an apparatus of the class described, a light source adapted toemit a light beam, a substantially U-shaped oscillating member bent of athin` metallic strip and including a plane front strip, two plane sidestrips, and-two plane fastening strips at the ends of said side strips,said side strips, being substantially normal to said front strip, andtheir length being substantially equal to the length of said front stripand the width of said front and side strips being from one half to onefifth of their length, said oscillating member arranged in such a mannerthat said front strip is in the path of and its face substantiallynormal to said light beam, a stationary support to which the free nds ofsaid fastening strips are firmly fastened in such a manner as to leavethe portions of said fastenl ing strips which are adjacent to said edgesbetween fastening and side strips, unfixed` to said late saidoscillating member in direction of the width of the strip of which it isbent.

normal to said lightbeam, a stationary support to whichithe tree euch o!said fastening strips arerigidlyfastenedinmchaminnerastoleave theportions of said fastening strips which are to one fifth of theirlength, said fastening strips' arranged at the ends of said side stripsat an angle of about with said side strips, forming thereby an -edgebetween said side strips and said fastening strips, said oscillatingmember being arranged in such a manner that said plane front strip is inthe path of s'aid light beam and its face is substantially normal tosaid light beam,

a stationary support to which both said fastening strips are rmly fixedin such a manner as to leave the portions of said fastening strips,which are adjacent to said edges between fastening and side strips,unxed to said stationary support, enabling thereby oscillation of vthesefree fastening strip'portions, and means adapted to oscillate saidoscillating member in direction of the width of the strip of which it isbent.

9. .In an apparatus of the class described, a light source adapted toemita light beam, a substantially U-shaped oscillating member bent of athin metallic strip and including a front strip, two side strips, andtwo fastening strips at the ends of said side strips, said oscillatingmember arranged in such a manner that said front strip is substantiallyin the path of andits face is substantially normal to said light beam, astationary support to whichthe free ends of said fastening strips arefirmly fastened in such a manner as to leave the portions of saidfastening strips which are adjacent to'- said edges between fasteningand side strips, unxed to said stationary support, mechanical dampingmeans arranged in contact with at least one of the faces of the sidestrips of said oscillating member, and means adapted to oscillate saidoscillate member in direction of the widthof the strip of which it isbent.

10. In an apparatus of the class described, a

light source adapted to emit a light beam, a substantially U-shapedoscillating member bent of a 'thin metallic strip and including a frontstrip,

two side strips, and two fastening strips at the ends of said sidestrips, said oscillating member arranged in such a manner that saidfront strip is substantially in the path of and its face is subof a thinmetallic strip, and including a'front f strip, two side strips, and twoyfastening strips at the ends of said` sideistrips, being substantiallyparallel tol said front strip, said member arranged in' the path of andsubstantially inone plane kwith said light beam, `a stationary supportto which` both ends of -said fasteningstrips `are irmly fastened in sucha. manner as to leave the portions of said fasteningj stripsv which areadjacent to `said edges between fasteningy and side strips,runiixe d tosaid stationary support, means for connectingsaidfastening strips withan elecstantially normal to said light beam, a stationary tric circuitthe` oscillations` ofwhich arefto be indicated or recorded, and apermanentmagnet arranged in such'a way as to form ,'in'thespace, where.the oscillating-member `is arranged,v a magnetic ileld having .itslines pf forcesubstantially parallel .tothe plane of the oscillatingmember, causing thus-oscillation of member correspondingv to th'e.current oscillations in the eleclating member in direction of the widthof the.

strip of which it is bent. Y

11. In an apparatus of the class described, a

light source adapted to emit a light beam, a sub- .v Y

is substantially in the path of and its face is substantially normal tosaid` light beam, a stationary support to which the free ends of saidfasten;

' ing strips are firmly fastened in such a manner as to leavetheportions of said fastening strips which are adjacent to said' edges.between fastening and side'strips, unflxed to said stationary support.at least one damping rubber'drop ad. A hering to said stationary supportand to at least one of the faces of the fastening strips of said cillate'said' oscillating member in direction of the width of the strip ofwhich it is bent.

l2. In a galvanometer of the class described, a

light source toemit a light beam, a substanthin .metallic strip, andincluding a front strip, two side strips, and'twofastening strips at theends of said side strips being substantially parallel to said frontstrip, said'member lbeing arranged in the path of and substantially inone plane with said light beam, a stationary support towhich both endsof said fastening strips are firmly fastened in such a manner as toleave the portionsofrsaid fastening strips. whichl are adjacent to saidedges between fastening and side -be indicated or recorded, apermanentmagnet tric circuit vconnected tothe end portions of` saidfastening strips.. nl

14. In a galvanometer of the class described,

a light source,` adapted to emit a light beam, a' substantially U-shapedoscillating member bent of a thin metallic strip, and `including a frontstrip, twoside strips, and twoifastening `strips at the ends `of saidside strips being substantially parallel to said front strip, saidmember arranged in the' path of and substantially in one planewith saidlight beam, a stationary support towhich both ends'pf said fasteningstrips-are firmly fastened in such (a manner as toleave the portions ofsaid fastening strips which are adjacent to said edges `between,fasteningand side strips, un fixed to `said stationary support, meansfor connectlng they ends of said vfastening strips with anelectriccircuit the ',oscillations'of whichfare to and at' least' onepole shoe; Said magnet and pole shoes arranged in such a mannery as tocreate in oscillating member, andmeans adapted to os the space where theU -shaped ,oscillating `mem-- ber is arranged ammetic neld.. Y

. 15. Ina galvanometer systemior soundrecordingby modulating a light inaccordance with the sound oscillationstofbe recorded, `a'. lightsourceadapted to emit a ,light a.v carrierfor the v sound to"be produced, saidcarrier arranged inthe path'` of said light beam l tially U,shapedloscillating member bent of a l j and,` adapted to be moved uniformspeed,

`a substantially vUshaped member.

bent of 'al metallicfstipfkliddncluding a front strip; two4 *sideVstrips.) 'and two fastening StriP'St 'the .ends 0f.. Sidslde Sttips'beissen# stantianyparanel msgid rrvontstia said front 'strip' being-providedfac one ofitsdses with cuistrips, unnxedto said stationarysupport, meansV for connectingsaid fastening strips an lelec,

variable areafsouaafredrdsab be prod'cedfsaid U-shaped oscillatingmember arranged between te maligni beams lwynncnf the free ends of saidfastening strips are firmly fastened in such a manner as to leave theportions of said fastening strips which are adjacent to said edgesbetween fastening and side strips, unxed to said stationary support, andmeans adapted to oscillate said oscillating member in direction of thewidth of the strip of which it is bent. 16. In a galvanometer system forsound recording by modulating a light beam in accordance with the soundoscillations to be recorded,

a light source adapted to emit a light beam, a I

carrier for the sound records to be produced, said carrier arranged inthe path of said light beam and adapted to be moved with uniform speed,a substantially U-shaped oscillating member bent of a thin metallicstrip and including a front strip, two side strips, and two fasteningstrips at the ends of said side strips being substantially parallel tosaid front strip, said U-shaped member arranged in such a manner thatsaid front strip is in the path of and its face is substantially normalto said light beam, a member forming a slit substantially parallel tosaid front strip and arranged in the path of said light beam between thelight source and said U-shaped member, a stationary support to whichboth ends of said fastening strips are firmly fastened yin such a manneras. to leave the portions of said fastening strips which are adj acentto said edges between fastening and side strips, unlxed to saidstationary support, means for connecting the ends of said fasteningstrips with an electric circuit the oscillations of which are to beindicated or recorded, a permanent magnet and two pole shoes, saidmagnet and said pole shoes 4arranged in Asuch a manner as to create inthe space where the oscillating member is arranged a magnetic eld havingits lines of force substantially parallel to the plane of this mem- 2'0ber.

FRANZ G. BACK.

